In vehicle brakes, at least one rotor connected to a wheel is braked by friction elements to be applied to the rotor during brake actuation. In drum brakes, brake shoes are radially and tangentially moved towards the rotating brake drum, the brake shoes being arranged inside the brake drum and spread by means of a cam in fixed connection with a camshaft, which camshaft is set into rotation by a lever of an actuating mechanism. The configuration of the cam could be in the form of a S-cam, Z-cam or any other well-known profiles.
At one of its axial ends the camshaft is connected to the lever of the brake actuator by means of a splined connection to enable a rotatably fixedly connection between these elements. At its opposite end, the camshaft comprises the cam profile for actuating the brake shoes so that upon rotation of the camshaft these do radially converge towards the inner surface of the rotating brake drum and finally engaging therewith.
The brake lever setting the camshaft into rotation usually comprises an automatic brake adjuster mechanism for compensation of the wear of the brake shoes and of the inner friction surface of the brake drum. Such automatic brake adjuster mechanism is built in the housing of the brake lever and is configured to create a relative displacement between the lever arm and inner parts of the automatic brake adjuster mechanism which are connected to the camshaft. The produced displacement corresponds to the actual wear of the brake linings and of the friction surface inside the brake drum.
To preclude malfunction of the drum brake mechanism, for safety reasons it is necessary to monitor the wear status of the entire mechanism.
For that purpose it is known to use wear monitoring devices which are attached to the end of the camshaft opposite of the cam, i.e. at the end which faces away from the brake drum. Such sensors are known with different configurations and are designed to either produce alarm signals when the wear of the brake linings and the brake drum exceeds a certain value predetermined to constitute a critical threshold or to produce continuously signals to superior monitoring control systems in the vehicle, which signals resemble the actual wear status.
Commonly known wear monitoring devices are known from e.g. publication U.S. Pat. No. 5,253,735 and WO 96/41970 of the applicant.
Such wear monitoring devices basically consist of a housing in which a rotating element is rotatably supported. The rotating element, usually in the form of a disc will be rotatably fixedly connected to the camshaft, whereby the housing remains stationary with respect to the rotating element and thus the camshaft. The housing of the wear monitoring device therefore has somehow to be mounted in a position which is fixed relative to the rotatable camshaft. The sensing mechanism to be employed in such wear monitoring devices could be of any known kind, like e.g. Hall devices, coded discs, potentiometers etc.
The camshaft comprises for its rotatably fixedly connection to the lever and to its corresponding part of the built-in automatic brake adjuster mechanism a splined section with splines which are uniformly distributed around the circumference of the camshaft. These splines are normally used for rotational fixation of the rotating element of the wear monitoring device to the camshaft as well. Alternatively, the rotating element could be clamped somehow to the periphery of the camshaft.
The rotating element constitutes the input part for the actual sensor arranged inside the housing of the wear monitoring device and its rotations reflect the rotations of the camshaft both during brake actuation and release on the one hand and the turns initiated by the automatic brake adjuster mechanism of the brake lever during automatic adjustment on the other.
It becomes obvious that the assembly of the wear monitoring device, in particular its installation at the camshaft requires properly aligned adjustments between the rotating element and the camshaft since otherwise there exists the risk that the wear monitoring device could deliver erroneous information about the actual wear status which thus could lead do safety hazards.
As this has to be performed manually, this in turn speaks for personnel which has to practice certain skills and which requires peculiar training for that purpose. Thus, assembly of the wear monitoring devices for drum brakes as known from the prior art both for installation and servicing will be time consuming associated with higher costs. Still then it cannot be avoided that the final installation is erroneous with respect to the alignment between the respective components.